Elevated levels of NO and CO in exhaled breath have been implicated as markers of airway inflammation in asthma. Combined with simultaneous measurements of exhaled CO2, Physical Sciences Inc. (PSI) proposes to develop a compact, low-cost sensor capable of dynamic, volume-resolved analysis of a single human breath. This capability will allow, for the first time, simultaneous measurements of expired NO and CO, as well as accurate resolution of upper airway, lower airway, and alveolar breath fractions. The sensor is based on advanced, room-temperature mid-IR tunable diode laser absorption. In the Phase I program, PSI demonstrated ppb-level detection of NO in human breath. In the Phase II program, we will integrate compact optical cell geometry with multiple lasers to develop and test a multi-species breath analyzer for asthma grading. The Phase II program will be conducted in partnership with Los Gatos Research and the Harvard Medical School's Brigham and Women's Hospital.